In the Long Term Evolution (LTE, registered trademark), a communication method known as Orthogonal Frequency Division Multiplexing (OFDM) is used. In OFDM, a large amount of communication is possible by using multiple single carriers each of which has orthogonal relationship. Each of the single carriers is called a sub-carrier (SC) and a group of large number of SCs is called a component carrier (CC). When multiple users communicate with each other, simultaneous communication performed by multiple users is implemented by allocating, to each of the users, a resource block (RB) including SCs that are suitable for the communication for the users selected from among SCs in a CC.
In OFDM, a mobile wireless terminal estimates the state of a channel used for a wireless transmission path by using a reference signal (RS) including already known data sent from a base station. Then, the mobile wireless terminal performs, on a signal received from the base station, an equalization process, a demodulation process, a decoding process, and the like. These processes are usually performed by the period (in LTE, 1 millisecond) called by a subframe.
Furthermore, the mobile wireless terminal measures the state of a channel used for a wireless transmission path for each SC and reports, to the base station, channel quality indicator (CQI) that indicates the quality of the estimated wireless transmission path at a predetermined unit of frequency. The base station sends, to the mobile wireless terminal on the basis of the CQI reported from the mobile wireless terminal, data by using an RB that includes SCs that have higher quality.
Patent Document 1: Japanese Laid-open Patent Publication No. 2010-11063
Patent Document 2: Japanese Laid-open Patent Publication No. 2010-213007
However, because RSs sent from the base station are allocated in a subframe in a distributed manner, channel estimation by using the RSs is difficult to be performed until the entirety of the subframe is received. Furthermore, because the equalization process, the demodulation process, or the like are not performed unless the channel estimation has been completed, signals received during this period are stored in a reception buffer.
If the number of RBs allocated to data transmission becomes great, an amount of data received in a subframe duration becomes great. Furthermore, in LTE-advanced that is the revision of LTE, carrier aggregation (CA) in which communication is performed by using multiple CCs (a maximum of 5 CCs) or multiple input multiple output (MIMO) in which communication is performed by using multiple antennas is used. With this method, in LTE-advanced, an amount of data that can be received by the mobile wireless terminal is further increased and an amount of data to be held until the channel estimation has been completed becomes further increased. Furthermore, in LTE-advanced, because a process of removing interference received from another base station is further added, the timing at which a process, such as a demodulation process or the like, can be started is further delayed and thus an amount of data needs to be held is further increased.
It is conceivable that data received before the completion of the channel estimation is held in an internal memory in a communication processor that controls the wireless communication. However, if an amount of the internal memory that is mounted on the communication processor is increased, a cost of the communication processor is increased. To avoid this problem, it is conceivable to increase, by arranging an external memory, such as an SDRAM or the like, outside the communication processor, a memory area that stores therein the reception data until the channel estimation has been completed. However, electrical power needed to read and write data used for an access to the external memory arranged outside the communication processor is greater than that used for an access to a memory that is arranged inside the communication processor. Consequently, in the receiving process, the electrical power consumed by the mobile wireless terminal is increased.